It is well known that certain battery cell chemistries, lithium ion for example, are susceptible to overcharging and to over-discharging operational problems. Overcharging and over-discharging issues can be in terms of the total state-of-charge or (SOC) in the rate of charge or rate of discharge. Occurrences of these conditions and other events can cause a reduced useful battery life. In the extreme, destructive mishaps involving intense heat, fire, and even explosion can occur. Avoiding such affects is particularly relevant when batteries of many cells are used with safety implications. In proximity to human activity is one example.
It is known to have electronic monitoring and control of state-of-charge and of temperature on a cell-by-cell basis. Control can affect overall charging/discharging characteristics and in many systems can reduce or increase the charge in individual cells via cell balancing.
It is also known to introduce a degree redundancy or back-up monitoring functionality in battery management systems to reduce the probability that one electronic failure will leave the battery and charging system in a state that allows, or even engenders, a significantly destructive cell mishap.
Electric vehicles (EV), Hybrid Electric Vehicles (HEV), and electric grid-stabilization are important examples of applications requiring a large number of lithium-ion cells. With cells connected in series, these batteries can have potential of over 300 volts. For safety from electrical hazard, safety from electrochemical fault effects, and to prevent tampering by untrained people, the cells are generally well contained within an enclosed “pack”. A pack is a secure container with a limited, protected, set of high-voltage connections. The pack generally includes the majority of the electronics associated with the battery management system and control logic as well as the cells themselves. An EV or HEV pack is intended to only be opened and repaired at a qualified center. A pack swap-out with a refurbished pack or other pack maintenance action can cost a significant fraction of the value of a vehicle. It is therefore desirable to avoid or minimize the need for pack maintenance due to electronic failure. While a triple-redundant system might be able to provide a degree of that capability, it would do so at a cost that might be prohibitive.
A system that could cost-effectively reduce the frequency of battery pack replacement in an EV from once in a vehicles life to never in a vehicles life, for example, would make a significant reduction in the projected lifetime cost of such vehicles.